High-frequency inductive structure



Feb 1951 M. J. COLUMBE HIGH-FREQUENCY INDUCTIVE STRUCTURE Filed Aug. 28, 1947 Inventor Patented Feb. 13, 1951 HIGH-FREQUENCY INDUCTIVE STRUCTURE Maynard J. Colombo, Schenectady, N. 2., assignor to General Electric Company, a corporation of New York Application August 28, 1947, Serial No. 770,985

4 Claims. (01. 175-359) My invention relates to a high frequency inductive structure and, more particularly. to a high frequency transformer suitable for energizing filaments of electron discharge devices that operate at high potentials with respect to ground.

Many problems have been presented in the development of high potential electron devices. such as electron and X-ray defraction instruments, electron microscopes, magnetrons, etc. One problem has been the development of adequate means for energizing the filaments of electron discharge devices used in such equipment that operate at a h gh potential with respect to ground. In the past, several methods have been employed for heating these filaments, for example: Batteries, 60 cycle transformers and radio frequency transformers. Batteries are objectionable in that they are too bulky and have a short life which necessitates frequent replacements. The 60 cycle transformer presents severe insulation problems and it is quite bulky and requires considerable space. The radio frequency transformer has proven the most satisfactory as it can be constructed in a minimum oi space and at a low cost. However, it also presents problems in insulation and construction.

Heretofore, where the primary and secondary windings of the radio frequency transformer have both been embedded in the insulating material, considerable difficulty was encountered due to the heating of the primary winding causing a breakdown of the insulation material. Voids develop and in operation the air in these voids becomes ionized and the internal corona gradually destroys the insulating material, causing losses or in some cases a complete breakdown. By eliminating the electrostatic coupling between the primary and secondary coils, the primary coil may be placed outs de of the insulating material. This is accomplished by a grounded electrostatic shield, commonly known as a Faraday shield, placed between the two windings.

' It is a general ob ect of mv invention to provide an improved high potential transformer.

Another object of my invention is to provide a high frenuency transformer suitable for operation at high potentials above ground.

A further obiect is to provide an improved high frequency transformer that is simple, compact and easy to manufacture.

A further ob ect of my invention is to provide a transformer with negligible ca acitive. cmmling between the primary and secondary windin s.

The features of my invention, which I believe to be novel, are set forth with articularity in the appended claims. My invention itself, however, together with further object and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawing in which Fig. 1 is a vertical view of a transformer suitably embodying the invention; Fig. 2 is a top view of the apparatus of Fig. 1; and Fig. 3 is a schematic diagram of an oscillating circuit combined with a transformer embodying my invention.

Referring now to Fig. 3, I have shown a transformer embodying my invention together with an oscillator circuit which energizes the primary windin thereof. For illustration, I have shown an oscillator circuit of the Hartley ty e. However, any other suitable circuit may be used. I have shown an electron dischar e d vi e it having an anode I 5, cathode l6, control grid l1 and.

screen gr d l8. The cathode I6 is connected to ground through the res stor l9 which is bypassed by capacitor 20. The high potent al a ode supply is designated by the convent onal symbol 3+ and is connected to t e anode i5 through a choke 2| and is b -passed to ground bv apacitor 22. A screen grid drooping re istor 23 is connected bet een the s reen ri in and 3+. One

end of a t ned circu t. compris n a c acitor 24 and an inductance I0, is connected to the anode through a blocking ca acitor 25. The other end of the tuned circuit is connected to the control grid il. The inductance Iii has a tan 2! and a portion of the winding is connected in the grid circuit to furnish feed back stabilization.

The inductance III also serves as a primary wind ng for the transformer 4. The secondary windin 6 is emb dded in a block 5 of suit ble insulating material. An ele"trostatic shield 8 is inserted between the primary wind ng i0 and secondarv winding 8 and is connect d to ground by the term nal 8. A cananitor 28 is connected across the secondarv windi g 6 for tuning.

Referrin now to Fig. 1 for a more detailed showing of the transformer and its con truction, I have shown a molded block or envelo e 5 which may be of any su table insulating mater al such as resinous compound mica, glass or the like. In the embodiment I have found that a resinous compound, such as polyethylene, has been particularly satisfactory as it has good molding qualities. The secondary winding 6 is molded into the envelope 5 and has its two ends brought out and terminated in a co-axial connector I. The electrostatic shield 8 is also embed ed in the envelo e 5 and is substant ally parallel to the secondary winding 6. The spac ng between the secondary winding 8 and the shield 8 is dependent upon the potential that will be impressed upon the winding 6. It is preferred that the portion of the envelope 5 between the winding 6 and the shield 8 be solid and contain no voids. The primary winding l shown to be helicaliy coiled, is mounted outside of the envelope by the plate H which is held in place by spacers l4, bolts l2 and nuts I3.

The secondary winding 6 consists of a single turn of large cross-section wire for low resistance. It is easily molded in the insulating material. Preferably it is constructed by first making a loop of almost 360 degrees, the two ends being folded back toward the center of the loop then being bent back perpendicular so as to terminate in a coaxial connector. Since the electrostatic shield is flat, it is adaptable to being molded into the surface of the insulating material. The dimensioning of the winding 8 and shield a to occupy substantially parallel planes facilitates mounting of these elements in the solid mass of insulating material while providing a simple, in-

expensive construction. The oscillator discharge device and its associated circuit components may be mounted on a transformer itself or may be placed some distance away. In the embodiment illustrated, the inductance of the oscillator circuit is used as a primary of the transformer. However. the oscillator may be used to excite the circuit of an amplifier and the primary of the transformer may then be connected in the plate circuit of the amplifier.

The coupling between the primary and secondary windings is dependent upon the adjustment of the respective windings for stable oscillator operation and suitable transfer of energy. The load (which may or may not be tuned) may be any electron tube filament, rectifier filament, cathode ray filament. electron gun filament or any other similar load which is at high potential with respect to ground.

The purpose of the electrostatic shield is to isolate the primary and secondary windings with respect to capacitive coupling so that a high voltage charge will not build up in any air space between the two. It is necessary only to insure that no air spaces exist between the electrostatic shield and the secondary winding. Since the shield is at ground potential, no corona can form between the primary and the shield. Hence, the primary may have air space which permits better cooling.

Among the advantages of the transformer constructed in accordance with my invention, are the reduction in radio frequency power losses. especiallv losses in the windings. Other advanta es reside in the fact that this transformer is simple, takes little space and can be manufactured at low cost.

While I have illustrated and described particular embodiments of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency inductive device comprising a. primary winding, a secondary winding inductively coupled to said primary winding, an electrostatic shield interposed between said windings, a solid mass of insulating material, said secondary winding and said electrostatic shield being dimensioned to occupy substantially parallel planes and being embedded in physical contact with said mass, and means for physically supporting said primary winding outside said mass and in spaced relationship with respect to said secondary winding.

2. A transformer adapted to have a high potential imposed thereon comprising a primary winding, a secondary winding, an electrostatic shield interposed between said windings, said secondary winding and electrostatic shield being dimensioned to occupy substantially parallel planes, a solid mass of insulating material, said secondary winding and said electrostatic shield being embedded in physical contact with said insulating material, means for physically supporting said primary winding outside said material and adjacent to said electrostatic shield and said secondary winding, whereby said windings are inductively coupled.

3. A high frequency transformer comprising a primary winding, a secondary winding inductively coupled to said primary winding, an electrostatic shield interposed between said windings, said secondary winding and electrostatic shield being dimensioned to occupy substantially parallel planes, a block of insulating material, said secondary winding and said electrostatic shield being embedded in physical contact with said block, a portion of said block separating said secondary winding and said shield, and means for physically supporting said primary winding in air outside of said block of insulating material and in spaced position with respect to said secondary winding.

4. A high frequency transformer arrangement comprising a high voltage winding and a low voltage winding, an electrostatic shield, said shield being embedded in physical contact with a solid electrical insulating material, said low voltage winding being embedded in physical contact with said material on one side of said shield, said shield and said low voltage winding being dimensioned to occupy substantially parallel planes, means for physically positioning said high voltage winding on the other side of said shield in spaced relation and magnetic coupling arrangement with said low voltage winding and substantially physically isolated from said material.

MAYNARD J. COLUMBE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,320,980 Bowman Nov. 4, 1919 1,558,090 Howard Oct. 20, 1925 1,651,922 Hughes Dec. 6, 1927 1,781,776 Capps Nov. 18, 1930 1,837,245 Wheeler Dec. 22, 1931 1,873,049 Schrader Aug. 23, 1932 1.930.604 Bahrmann Oct. 17, 1933 2,085,434 Loftis et a1 June 29, 1937 2,280,625 Camilli Apr. 21, 1941 2,318,271 Weiche May 4, 1943 2,381,278 Gregory et a1 Aug. 7, 1945 2,413,195 Schwager Dec. 24, 1946 FOREIGN PATENTS Number Country Date 328,772 Great Britain May 8, 1930 753,486 France Oct. 17, 1933 

